Valve actuators find wide application and are notably used in conventional refuelling systems onboard aircrafts.
The valve actuators generally all have processor control for setting, monitoring and controlling the actuator. Key control factors include actuator position, i.e. valve position, and actuator torque (primarily for rotary output actuators) and thrust (primarily for linear output actuators). In a rotary output actuator, for example, valve position is typically determined by counting the revolutions or part of a revolution of the driven rotary output shaft by a rotary encoder. The load generated at the actuator output shaft in such an actuator is typically determined by mechanical means, such as by a strain gauge or by a pressure transducer. Load might also be determined from a torque related current in the motor.
Moreover, the valve actuators generally also have facility for failsafe if, for example, there is an electrical power failure. To this end, the majority of actuators further incorporate a compression spring return mechanism to restore the actuator to the desired failsafe position.
Nevertheless, this type of valve actuator presents the drawback of providing a water hammer in case of overpressure.
Moreover, in refuelling system of aircrafts, these valve actuators allow only a general regulation as disclosed in the document US2008/0173762. This document discloses an aircraft refuelling system allowing the refuelling rates to be increased, in which fuel flow restrictors are mounted in the refuelling pipework of the aircraft and restrict the flow rate of fuel from the refuelling pipework into the fuel tanks. Fuel valves are also provided to allow each tank to be disconnected from the refuelling pipework. A general regulation is performed by a fuel pressure regulator on board the aircraft so as to define the maximum pressure in the refuelling pipework. This kind of general regulation is not adapted when there is a need to more refuelling a specific fuel tank. The onboard fuel circuit of an aircraft thus cannot be always optimized according to the concrete needs.
Therefore, a need exists for a valve actuators avoiding water hammer when an overpressure appears and allowing a new way of refuelling the respective fuel tanks of an aircraft notably.